Re: [PATCH v4 3/3] r8169: fix the KCSAN reported data race in rtl_rx while reading desc->opts1

[Simon Horman]

On Wed, Oct 18, 2023 at 09:34:38PM +0200, Mirsad Goran Todorovac wrote:
> KCSAN reported the following data-race bug:
> 
> ==================================================================
> BUG: KCSAN: data-race in rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4430 drivers/net/ethernet/realtek/r8169_main.c:4583) r8169
> 
> race at unknown origin, with read to 0xffff888117e43510 of 4 bytes by interrupt on cpu 21:
> rtl8169_poll (drivers/net/ethernet/realtek/r8169_main.c:4430 drivers/net/ethernet/realtek/r8169_main.c:4583) r8169
> __napi_poll (net/core/dev.c:6527)
> net_rx_action (net/core/dev.c:6596 net/core/dev.c:6727)
> __do_softirq (kernel/softirq.c:553)
> __irq_exit_rcu (kernel/softirq.c:427 kernel/softirq.c:632)
> irq_exit_rcu (kernel/softirq.c:647)
> sysvec_apic_timer_interrupt (arch/x86/kernel/apic/apic.c:1074 (discriminator 14))
> asm_sysvec_apic_timer_interrupt (./arch/x86/include/asm/idtentry.h:645)
> cpuidle_enter_state (drivers/cpuidle/cpuidle.c:291)
> cpuidle_enter (drivers/cpuidle/cpuidle.c:390)
> call_cpuidle (kernel/sched/idle.c:135)
> do_idle (kernel/sched/idle.c:219 kernel/sched/idle.c:282)
> cpu_startup_entry (kernel/sched/idle.c:378 (discriminator 1))
> start_secondary (arch/x86/kernel/smpboot.c:210 arch/x86/kernel/smpboot.c:294)
> secondary_startup_64_no_verify (arch/x86/kernel/head_64.S:433)
> 
> value changed: 0x80003fff -> 0x3402805f
> 
> Reported by Kernel Concurrency Sanitizer on:
> CPU: 21 PID: 0 Comm: swapper/21 Tainted: G             L     6.6.0-rc2-kcsan-00143-gb5cbe7c00aa0 #41
> Hardware name: ASRock X670E PG Lightning/X670E PG Lightning, BIOS 1.21 04/26/2023
> ==================================================================
> 
> drivers/net/ethernet/realtek/r8169_main.c:
> ==========================================
>    4429
>  → 4430                 status = le32_to_cpu(desc->opts1);
>    4431                 if (status & DescOwn)
>    4432                         break;
>    4433
>    4434                 /* This barrier is needed to keep us from reading
>    4435                  * any other fields out of the Rx descriptor until
>    4436                  * we know the status of DescOwn
>    4437                  */
>    4438                 dma_rmb();
>    4439
>    4440                 if (unlikely(status & RxRES)) {
>    4441                         if (net_ratelimit())
>    4442                                 netdev_warn(dev, "Rx ERROR. status = %08x\n",
> 
> Marco Elver explained that dma_rmb() doesn't prevent the compiler to tear up the access to
> desc->opts1 which can be written to concurrently. READ_ONCE() should prevent that from
> happening:
> 
>    4429
>  → 4430                 status = le32_to_cpu(READ_ONCE(desc->opts1));
>    4431                 if (status & DescOwn)
>    4432                         break;
>    4433
> 
> As the consequence of this fix, this KCSAN warning was eliminated.
> 
> Fixes: 6202806e7c03a ("r8169: drop member opts1_mask from struct rtl8169_private")
> Suggested-by: Marco Elver <elver@xxxxxxxxxx>
> Cc: Heiner Kallweit <hkallweit1@xxxxxxxxx>
> Cc: nic_swsd@xxxxxxxxxxx
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Link: https://lore.kernel.org/lkml/dc7fc8fa-4ea4-e9a9-30a6-7c83e6b53188@xxxxxxxxxxxx/
> Signed-off-by: Mirsad Goran Todorovac <mirsad.todorovac@xxxxxxxxxxxx>
> Acked-by: Marco Elver <elver@xxxxxxxxxx>

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>